34th Conference on Radar Meteorology


The where and why of tropical thick anvil

Wei Li, Texas A&M University, College Station, TX; and C. Schumacher

The vertical structure of reflectivity observed by the Tropical Rainfall Measuring Mission (TRMM) Precipitation Radar (PR) and CloudSat Cloud Profiling Radar (CPR) was used to investigate the geographical distribution and temporal variability of tropical anvil (i.e., thick, non-precipitating cloud associated with deep convection). Based on 10 years of TRMM measurements from 1998 to 2007, anvil observable by the PR occurs on average 5 out of every 100 days within grid boxes of 2.5° resolution and has an overall areal coverage of 0.2% across the tropics; this anvil also has an average echo top ~8.5 km and an average thickness ~2.7 km. In order to quantify the amount of anvil that the PR is missing, coincident PR/CPR overpasses were examined. Statistics show that the TRMM PR underestimates anvil top height by an average of ~5 km and underestimates the horizontal extent by an average factor of 4 compared to the CPR.

Tropical anvil occurs most often in regions of large rain accumulation over both land and ocean, but covers disproportionately larger areas over West and Central Africa and other land regions. It appears that more anvil is created per unit convection over land than over ocean. Anvil is also higher and thicker over land than over ocean, which is consistent with observations that show anvil-producing convection over land tends to have higher echo tops and stronger near-surface reflectivities than anvil-producing convection over ocean. Some tropical land regions, especially those affected by monsoon circulations, experience significant seasonal variability in anvil properties. Strong interannual anvil variability occurs over the central Pacific due to the El Niņo-Southern Oscillation. Therefore, the characteristics and occurrence of the parent convection are important factors in describing the climatology of thick anvil across the tropics. Large-scale environmental factors, such as strong upper-level wind shear, also appear to assist the generation of anvil and can in part explain the different anvil statistics over land and ocean. The ability to observe and model the occurrence and vertical extent of anvil is essential in capturing the energy and water budget of the tropics.

Poster Session 7, Spaceborne Radar
Tuesday, 6 October 2009, 1:30 PM-3:30 PM, President's Ballroom

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